Fabled Northwest Passage begins to re-freeze

This summer's dramatic loss of Arctic sea ice peaked on September 15, and the polar ice cap is finally beginning to re-freeze, according to a press release issued by the National Snow and Ice Data Center on October 1. Extent of the September polar sea ice fell 39%, compared to the 1979-2000 average. To put this loss in perspective, in one year we lost as much ice as we lost during the previous 28 years. Summertime Arctic sea ice is now at 50% of what it was in the 1950s (Figure 1). One may look at at graph and wonder, but what about sea ice loss in other seasons? It hasn't been nearly so severe. True, but it is the summer ice we care most about, since summer is when the thick, multi-year ice melts, which can then precondition the Arctic for much greater ice loss in future years. As sea ice melts in response to rising temperatures, more of the dark ocean is exposed, allowing it to absorb more of the sun's energy. This further increases air temperatures, ocean temperatures, and ice melt in a process know as the "ice-albedo feedback" (albedo means how much sunlight a surface reflects). There is an excellent chance that the summer of 2007 will be remembered as the "tipping point" for Arctic sea ice, when an irreversible ice-albedo feedback process firmly established itself.

Northwest Passage opens for the first time in recorded historyLong before the Panama and Suez Canals made commercial trading between the Atlantic and Pacific Oceans economically feasible, ships made the long and perilous trip around the African and South America continents. Explorers, traders, and world leaders looking for faster and less dangerous shipping routes to far-away areas of the world have long eyed two routes through the ice-choked Arctic Ocean--the fabled Northwest Passage, through the cold Arctic waters north of Canada, and the Northeast Passage, extending along the northern coast of Russia. The first recorded attempt to find and sail the Northwest Passage was in 1497, and ended in failure. The thick ice choking the waterways thwarted all attempts at passage for the next four centuries. Finally, in 1905, Roald Amundsen completed the first successful navigation of the Northwest Passage. It took his ship two-and-a-half years to navigate through narrow passages of open water, and his ship spent two cold, dark winters locked in the ice during the feat. More recently, icebreakers and ice-strengthened ships have on occasion battered their way through the ice-blocked route.

Figure 2. The Northwest Passage shipping route (red line) and Northeast Passage (green line) superimposed on an ice coverage map from August 22, 2007. The Northwest Passage was ice-free and navigable for 36 days between August 14 and September 18, 2007. The Northeast Passage was blocked by a narrow strip of ice most of the summer. Image credit: National Snow and Ice Data Center.

Times are changing. In 2001, the Bering Strait, a key portion of both the Northwest and Northeast Passages, was completely ice free. This was followed in 2005 by record-breaking sea-ice melt in the Arctic, leading to the first ever recorded opening of the Northeast Passage. The fabled Northwest Passage remained closed in 2005. Arctic ice recovered a bit in 2006, and both passages remained closed. But the unprecedented melting during the summer of 2007 saw the Northwest Passage become ice-free and navigable along its entire length without the need for an icebreaker as of August 14, 2007. Remarkably, the Northwest Passage remained ice-free for 36 days, finally refreezing over a small section on September 19. The Northeast Passage was blocked by a narrow strip of ice all summer. However, this strip of ice thinned to just 30% coverage on September 25 and 26, making the Northeast Passage passable for ordinary ships on those days.

When is the last time the Northwest Passage was open?We can be sure the Northwest Passage was never open from 1900 on, as we have detailed ice edge records from ships. It is very unlikely the Passage was open between 1497 and 1900, since this was a cold period in the northern latitudes known as "The Little Ice Age". Ships periodically attempted the Passage and were foiled during this period, and the native Inuit people have no historical tales of the Passage being navigable at any time in the past.

A good candidate for the last previous opening of the Northwest Passage was the period 5,000-7,000 years ago, when the Earth's orbital variations brought more sunlight to the Arctic in summer than at present. Prior to that, the Passage was probably open during the last inter-glacial period, 120,000 years ago. Temperatures then were 2-3 degrees Centigrade higher than present-day temperatures, and sea levels were 4-6 meters higher.

Final thoughtsIf we have reached the tipping point for Arctic ice, what are the implications? I'll discuss this more in a future blog. Sea ice is very complicated, and it is not a sure thing that we have reached the tipping point. For more on the complexities of sea ice, read wunderblogger Dr. Ricky Rood's latest blog.

NASA has posted a beautiful satellite image of the Arctic ice cap at the September 15 2007 minimum, showing the open water of the Northwest Passage.

I thank Edalin Michael of the University of Michigan's School of Natural Resources and Robert Grumbine of NOAA's Sea Ice Group for their contributions to this blog.

After all, if there was climate change 700 years ago, or a thousand years ago, or two thousand years ago, etc. -- and, we know such change occurred, hence the "Ice Age" and "Little Ice Age", etc. -- and if such change occurred before the Industrial Revolution, then why assume today's climate change is the result of man's activities when the climate change throughout the 99.99999999% of earth's history could not have been caused by man.

I think GW could be a problem. I was outside mowing my grass with a GAS mower and was thinking. "Well should i buy an electric mower or put a fence an buy some goats." Didn't think my liberal neighbor would perfer the goats....lol

Im not comparing seasons...I'm talking about being fooled with the trends of this season, alone. I understand this is above average activity in the longrun. I'm not saying the season was a bust by any means. I think its quite exciting to be witnessing the weather events and anomolies that we are. The exciting stuff isnt limited to the exact number of cyclones..but the behavior of these systems and the realization that there's so much we dont understand yet.

It is a planet where global warming isn't happening -- or, if it is happening, isn't happening because of human beings. Or, if it is happening because of human beings, isn't going to be a big problem. And, even if it is a big problem, we can't realistically do anything about it other than adapt.

A quote from the story you linked to HH...the skeptics are as bad as the alarmists; my point is that going all the way to one camp or the other makes no sense at all. Somewhere in this morass of science and pseudo science is the answer, but given the hype generated by both sides it's impossible to tell...

To me Al Gore is just a whistleblower on a topic that is created by man

"Global Warming" is a term that was created in the last few years, to describe what is going on

Im sorry but 30 years, 100 years or 200 years worth of record keeping on how the ice in Antarctica is melting, is no proof of Global Warming, because there is absolutely no way to tell that this rate of melting didnt happen thousands of years ago to

TPW - Total Precipitable Water is an excellent product of measuring low level water vapor as the water vapor imagery of Geostationary satellites that we normally use only measure mid-upper level water vapor and is mostly use to track mid-upper level plumes and features. TPW is calculated by assuming that all the water vapor in a coloum of the atmosphere is condensed and then collected at ground and measured.

The Image below some features that can be identified are:

The ITCZ over the tropical Atlantic.

The trade wind inversion (low values in the Atlantic north of the ITCZ.

TD 15

Very deep moisture in the NW Caribbean where ex-94L is located.

The long moisture plume extending from the NW Caribbean into the Atlantic is a surface trough and it clearly stands out.

Notice how the ITCZ curves northwards in the Eastern Caribbean....that is a tropical wave.

Most of these would not accurately positioned if used the normal water vapor imagery we used.

If I am reading this article correctly, winds, not temperature, were the "biggest" reason for Ice loss in the Arctic. I sent this information to Dr. Masters and asked for his comments, with no reply! :(

"Between winter 2005 and winter 2007, the perennial ice shrunk by an area the size of Texas and California combined. This severe loss continues a trend of rapid decreases in perennial ice extent in this decade. Study results will be published Oct. 4 in the journal Geophysical Research Letters.

The scientists observed less perennial ice cover in March 2007 than ever before, with the thick ice confined to the Arctic Ocean north of Canada. Consequently, the Arctic Ocean was dominated by thinner seasonal ice that melts faster. This ice is more easily compressed and responds more quickly to being pushed out of the Arctic by winds. Those thinner seasonal ice conditions facilitated the ice loss, leading to this year's record low amount of total Arctic sea ice.

Nghiem said the rapid decline in winter perennial ice the past two years was caused by unusual winds. "Unusual atmospheric conditions set up wind patterns that compressed the sea ice, loaded it into the Transpolar Drift Stream and then sped its flow out of the Arctic," he said. When that sea ice reached lower latitudes, it rapidly melted in the warmer waters.

"The winds causing this trend in ice reduction were set up by an unusual pattern of atmospheric pressure that began at the beginning of this century," Nghiem said."